MD11 CREW DEPARTING RKSI FORGETS TO SET QNE PASSING TRANSITION ALT.

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DEP FROM RKSI WAS UNEVENTFUL; FO FLYING CAPT MONITORING AND I WAS THE RELIEF PLT. INITIAL CLRNC WAS TO CLB TO FL290; RADAR 1A DEP. SUBSEQUENT RADAR VECTOR FOLLOWED BY DIRECT TO SEL AND G597. AFTER DEP I WAS CALCULATING TIMES FOR THE FLT AND HEARD ATC GIVE US A LEVELOFF AT FL150 INBOUND TFC AT FL160 WHICH WAS ACKNOWLEDGED BY THE CAPT. AS WE WERE APCHING FL150 THERE WERE SEVERAL CALLS FROM ATC TO ADVISE OF TFC AND LEVEL AT FL150 WHICH WE ACKNOWLEDGED; BUT ATC DIDN'T SEEM TO BE RECEIVING. THE FO ALSO RESPONDED. I WAS GETTING READY TO RESPOND ALSO. THE INBOUND TFC WAS ACQUIRED VISUALLY AND VISUAL SIGHTING WAS RPTED TO ATC. WHEN WE LEVELED AT FL150 IT WAS DISCOVERED THAT THE LCL ALTIMETER SETTING WAS STILL SET WHICH WAS 1003 HECTOPASCALS WITH A TRANSITION ALT OF FL140. THE ALTIMETERS WERE QUICKLY RESET WHICH SHOWED US 200-300 FT HIGH; THE AUTOPLT WAS DISCONNECTED AND AN AGGRESSIVE PUSH WAS INITIATED TO RETURN TO FL150. THE INBOUND TFC WAS STILL SEVERAL MI AWAY AND WE WERE BACK LEVEL AT FL150 WHEN THE INBOUND TFC PASSED. THERE WERE NO TCAS WARNINGS OR ALERTS. ATC CALLED AND ASKED WHY WE DIDN'T RESPOND TO RADIO CALLS AND SAID THAT WE HAD BEEN 300 FT ABOVE ALT. WE ADVISED ATC THAT WE HAD RESPONDED TO ALL THEIR RADIO CALLS AND HAD INADVERTENTLY BEEN DELAYED SETTING QNE WHICH CAUSED THE MOMENTARY ALTDEV. THE REMAINDER OF THE FLT WAS UNEVENTFUL.